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Cerebral blood velocity and other cardiovascular responses to 2 days of head-down tiltSpaceflight induces a cephalad redistribution of fluid volume and blood flow within the human body, and space motion sickness, which is a problem during the first few days of space flight, could be related to these changes in fluid status and in blood flow of the cerebrum and vestibular system. To evaluate possible changes in cerebral blood flow during simulated weightlessness, we measured blood velocity in the middle cerebral artery (MCA) along with retinal vascular diameters, intraocular pressure, impedance cardiography, and sphygmomanometry on nine men (26.2 +/- 6.6 yr) morning and evening for 2 days during continuous 10 deg head-down tilt (HDT). When subjects went from seated to head-down bed rest, their heart rate and retinal diameters decreased, and intraocular pressures increased. After 48 h of HDT, blood flow velocity in the MCA was decreased and thoracic impedance was increased, indicating less fluid in the thorax. Percent changes in blood flow velocities in the MCA after 48 h of HDT were inversely correlated with percent changes in retinal vascular diameters. Blood flow velocities in the MCA were inversely correlated (intersubject) with arterial pressures and retinal vascular diameters. Heart rate, stroke volume, cardiac output, systolic arterial pressure, and at times pulse pressure and blood flow velocities in the MCA were greater in the evening. Total peripheral resistance was higher in the morning. Although cerebral blood velocity is reduced after subjects are head down for 2 days, the inverse relationship with retinal vessel diameters, which have control analogous to that of cerebral vessels, indicates cerebral blood flow is not reduced.
Document ID
19930057125
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Frey, Mary A. B.
(NASA Lyndon B. Johnson Space Center Houston, TX, United States)
Mader, Thomas H.
(NASA Lyndon B. Johnson Space Center Houston, TX, United States)
Bagian, James P.
(NASA Lyndon B. Johnson Space Center Houston, TX, United States)
Charles, John B.
(NASA Lyndon B. Johnson Space Center Houston, TX, United States)
Meehan, Richard T.
(U.S. Army, Madigan Army Medical Center Tacoma, WA; Universities Space Research Association; NASA, Johnson Space Center, Houston; Texas Univ, United States)
Date Acquired
August 16, 2013
Publication Date
January 1, 1993
Publication Information
Publication: Journal of Applied Physiology
Volume: 74
Issue: 1
ISSN: 8750-7587
Subject Category
Aerospace Medicine
Accession Number
93A41122
Funding Number(s)
CONTRACT_GRANT: NIH-MO1-RR-00073
Distribution Limits
Public
Copyright
Other

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